Polycrystalline diamond material

ABSTRACT

A polycrystalline diamond material comprising a mass of diamond particles or grains exhibiting inter-granular bonding and a binder material comprises a non-metallic catalyst material for diamond, the non-metallic catalyst material for diamond comprising at least one nitrogen compound derived from an ammonium compound and/or at least one halide compound.

FIELD

This disclosure relates to polycrystalline diamond (PCD) material, andto a method of making such material.

BACKGROUND

Cutter inserts for machine and other tools may comprise a layer ofpolycrystalline diamond (PCD) bonded to a cemented carbide substrate.PCD is an example of a superhard material, also called superabrasivematerial, which has a hardness value substantially greater than that ofcemented tungsten carbide.

Components comprising PCD are used in a wide variety of tools forcutting, machining, drilling or degrading hard or abrasive materialssuch as rock, metal, ceramics, composites and wood-containing materials.PCD comprises a mass of substantially inter-grown diamond grains forminga skeletal mass, which defines interstices between the diamond grains.PCD material comprises at least about 80 volume % of diamond and may bemade by subjecting an aggregated mass of diamond grains to an ultra-highpressure of greater than about 5 GPa and temperature of at least about1,200 degrees centigrade in the presence of a sintering aid, alsoreferred to as a catalyst material for diamond. Catalyst material fordiamond is understood to be material that is capable of promoting directinter-growth of diamond grains at a pressure and temperature conditionat which diamond is thermodynamically more stable than graphite. Somecatalyst materials for diamond may promote the conversion of diamond tographite at ambient pressure, particularly at elevated temperatures.Examples of catalyst materials for diamond are cobalt, iron, nickel andcertain alloys including any of these. PCD may be formed on acobalt-cemented tungsten carbide substrate, which may provide a sourceof cobalt catalyst material for the PCD. The interstices within PCDmaterial may at least partly be filled with the catalyst material.

A well-known problem experienced with this type of PCD material,however, is that the residual presence of the catalyst material fordiamond, in particular a metallic catalyst material for diamond, forexample Co, Ni or Fe, in the interstices has a detrimental effect on theperformance of the PCD material at high temperatures. Duringapplication, the PCD material heats up and thermally degrades, largelydue to the presence of the metallic catalyst material that catalysesgraphitisation of the diamond and also causes stresses in the PCDmaterial due to the large difference in thermal expansion between themetallic catalyst material and the diamond microstructure.

One approach to addressing this problem is to remove, typically byleaching, the catalyst material, also referred to as a catalyst/solventin the art, from the PCD material.

U.S. Pat. No. 3,745,623 and U.S. Pat. No. 4,636,253 teach the use ofheated acid mixtures in the leaching process in which mixtures of HF,HCl, and HNO₃ and HNO₃ and HF, respectively, are used.

U.S. Pat. No. 4,288,248 and U.S. Pat. No. 4,224,380 describe removal ofthe catalyst/solvent by leaching the PCD tables in a hot mediumcomprising HNO₃—HF (nitric acid and hydrofluoric acid), alone or incombination with a second hot medium comprising HCl—HNO₃ (hydrochloricacid and nitric acid).

US 2007/0169419 describes a method of leaching a portion or all of thecatalyst/solvent from a PCD table by shielding the portion of the PCDtable not to be leached and immersing the shielded PCD table incorrosive solution to dissolve the catalyst/solvent in water and aquaregia. The leaching process is accelerated by the use of sonic energy,which agitates the interface between the PCD table and the corrosivesolution to accelerate the dissolution rate of the catalyst/solvent.

U.S. Pat. No. 4,572,722 discloses a leaching process that is acceleratedby forming a hole in the PCD table by laser cutting or spark emissionprior to or during the leaching process. The PCD table is then leachedby using conventional acid leaching techniques, electrolytic leachingand liquid zinc extraction.

An alternative approach to addressing the problem is to use anon-metallic catalyst material for diamond that produces a morethermally stable PCD material.

JP2795738 (B2) describes sintering a mixture of diamond powder and metalcarbonates at pressures of 6-12 GPa and temperatures of 1700-2500° C. togive sintered polycrystalline material consisting of 0.1-15 vol %non-metallic binder in a sintered diamond layer.

JP4114966 describes the use of carbon powder added as a sintering aid todiamond powder and an alkali earth carbonate, in order to improve thesinterability of the non-metallic system.

JP2003226578 also addresses the problem of poor sinterability, whichdescribes the use of oxalic acid dihydrate as a sintering aid in acarbonate-based non-metallic solvent/catalyst system.

JP2002187775 describes the addition of other organic compounds toachieve a sintered carbonate-based non-metallic PCD, and similarly theaddition of metal carbides is described in JP6009271.

SUMMARY

In general terms, this disclosure relates to comprises a polycrystallinediamond material having a non-metallic catalyst material for diamond.

Viewed from a first aspect there is provided a polycrystalline diamondmaterial comprising a mass of diamond particles or grains exhibitinginter-granular bonding and a binder material comprising a non-metalliccatalyst material for diamond, the non-metallic catalyst material fordiamond comprising at least one nitrogen compound derived from anammonium compound and/or at least one halide compound.

The ammonium compound may comprise an anion selected from the groupcomprising the carbonates, phosphates, hydroxides, oxides, sulphates,borates, titanates, silicates, halides, and combinations thereof.

The halide compound may comprise a cation selected from the groupcomprising the alkali metals, alkali earth metals, transition metals,ammonium, and combinations thereof.

In some embodiments, the non-metallic catalyst material for diamond maycomprise one or more of lithium chloride, sodium chloride, potassiumchloride, rubidium chloride, caesium chloride, magnesium chloride,calcium chloride, strontium chloride, barium chloride, yttrium chloride,zirconium chloride, zinc chloride, niobium chloride, all oxidationstates thereof, and mixtures thereof.

In some embodiments, the average particle size of the diamond particlesor grains may be from about 5 nanometres to about 50 microns, or fromabout 20 nanometres to about 20 microns, or from about 50 nanometres toabout 10 microns.

In some embodiments, the diamond content of the polycrystalline diamondmaterial may be at least about 80 percent, at least about 88 percent, atleast about 90 percent, at least about 92 percent or even at least about96 percent of the volume of the polycrystalline diamond material. In oneor more embodiments, the diamond content of the polycrystalline diamondmaterial may be at most about 98 percent of the volume of thepolycrystalline diamond material.

The content of the non-metallic catalyst material for diamond may, forexample, be at most about 20 volume percent, at most about 10 volumepercent, at most about 8 volume percent, or even at most about 4 volumepercent of the PCD material.

Viewed from a further aspect there is provided a method for makingpolycrystalline diamond material, the method including providing a massof diamond particles or grains, contacting the diamond particles orgrains with a binder material comprising a non-metallic catalystmaterial for diamond, the non-metallic catalyst material for diamondcomprising at least one ammonium compound and/or at least one halidecompound, consolidating the diamond particles or grains and bindermaterial to form a green body, and subjecting the green body to atemperature and pressure at which diamond is thermodynamically stable,sintering and forming polycrystalline diamond material.

In some embodiments, the salts may be combined with the diamondparticles or grains via infiltration, mixing, milling, chemical vapourdeposition, colloidal (sol-gel) deposition, atomic layer deposition,physical vapour deposition, and the like.

In some embodiments, the diamond particles or grains and the bindermaterial may be mixed in powder form with appropriate binding aids.

The diamond particles or grains may be suspended in a liquid medium, thenon-metallic catalyst material for diamond precipitating in situ ontothe surfaces of respective diamond particles or grains in the liquidmedium in order to coat the diamond particles or grains.

In some embodiments, the diamond particles or grains prior to contactwith the binder material may have an average particle or grain size offrom about 5 nanometres to about 50 microns, or from about 20 nanometresto about 20 microns, or from about 50 nanometres to about 10 microns.

In some embodiments, a multimodal mixture of diamond particles or grainsof varying average particle or grain size may be provided.

The polycrystalline diamond material may be a stand-alone compact or maybe attached to a substrate, such as a metal carbide substrate, forexample.

Sintering may be carried out at pressures of 4 GPa or more, or 7 GPa ormore, and temperatures of 1000° C. or more, or 1700° C. or more, forsintering times of 10 minutes or longer, or sintering times of 30seconds or longer, or one minute or longer.

In some embodiments, sintering may be carried out at pressures of 7 GPaor less and temperatures of 1800° C. or less.

According to another aspect, there is provided a wear element comprisinga polycrystalline diamond material as defined above.

Enhanced thermal stability of the polycrystalline diamond material overconventional metal catalysed polycrystalline material and lowersintering temperatures and pressures than for other non-metalliccatalyst materials for diamond may be obtained through one or moreembodiments.

DETAILED DESCRIPTION OF EMBODIMENTS

As used herein, “polycrystalline diamond” (PCD) material comprises amass of diamond grains, a substantial portion of which are directlyinter-bonded with each other and in which the content of diamond is atleast about 80 volume percent of the material. In one embodiment of PCDmaterial, interstices between the diamond grains may at least partly befilled with a binder material comprising a non-metallic catalyst fordiamond.

As used herein, “non-metallic catalyst material for diamond” is amaterial that is capable of catalysing intergrowth of polycrystallinediamond particles or grains under conditions of temperature and pressureat which diamond is more thermodynamically stable than graphite.

As used herein, “interstices” or “interstitial regions” are regionsbetween the diamond grains of PCD material.

A multi-modal size distribution of a mass of grains is understood tomean that the grains have a size distribution with more than one peak,each peak corresponding to a respective “mode”. Multimodalpolycrystalline bodies are typically made by providing more than onesource of a plurality of grains, each source comprising grains having asubstantially different average size, and blending together the grainsor particles from the sources. Measurement of the size distribution ofthe blended grains typically reveals distinct peaks corresponding todistinct modes. When the grains are sintered together to form thepolycrystalline body, their size distribution is further altered as thegrains are compacted against one another and fractured, resulting in theoverall decrease in the sizes of the grains. Nevertheless, themultimodality of the grains is usually still clearly evident from imageanalysis of the sintered article.

As used herein, a green body is an article that is intended to besintered or which has been partially sintered, but which has not yetbeen fully sintered to form an end product. It may generally beself-supporting and may have the general form of the intended finishedarticle.

As used herein, a superhard wear element is an element comprising asuperhard material and is for use in a wear application, such asdegrading, boring into, cutting or machining a workpiece or bodycomprising a hard or abrasive material.

A polycrystalline diamond material according to some embodimentscomprises diamond having increased thermal stability over conventionalsolvent/catalyst sintered diamond composite materials. In someembodiments, the polycrystalline diamond material includes a bindercomprising a non-metallic catalyst material for diamond. Thenon-metallic catalyst material for diamond comprises at least onenitrogen compound derived from an ammonium compound and/or at least onehalide containing compound.

A method for making polycrystalline diamond material, in someembodiments, includes contacting a mass of diamond particles or grainswith a binder material comprising a non-metallic catalyst material fordiamond. The non-metallic catalyst material for diamond is at least oneammonium compound and/or at least one halide compound.

The salts may be combined with diamond by, for example, infiltration,mixing, milling, chemical vapour deposition, colloidal (sol-gel)deposition, atomic layer deposition, physical vapour deposition andother similar processes that would be appreciated by those skilled inthe art.

The non-metallic binder material may be combined with the diamondparticles or grains in powder form. It can be mixed in a conventionalmixing process such as, for example, a planetary ball milling process,typically in the presence of a milling aid such as methanol, forexample. Milling balls, such as Co-WC milling balls, may be used to millthe binder and diamond powders together. The binder and diamond mixturemay then typically be dried at a temperature of 50 to 100° C. to removethe methanol and other volatile residues and then consolidated into agreen body ready for sintering.

In an alternative embodiment, the non-metallic binder material may becombined with the diamond particles or grains in a sol-gel process.Diamond powder is suspended in a liquid under vigorous stirring to forma diamond suspension. The liquid is typically water although the personskilled in the art will appreciate that any appropriate liquid mediumcan be used. A first salt of the desired ammonium cation and/or halideanion may be chosen such that it is soluble in a solvent, but forms aninsoluble salt with a chosen anion/cation, as the case may be, in thediamond suspension. A second salt of the desired anion/cation may bechosen such that it is soluble in a solvent, but the anion/cation formsan insoluble salt respectively with the ammonium cation and/or halideanion of the first salt.

The two salt containing solutions are added concomitantly drop wise tothe diamond suspension such that an insoluble precipitate consisting ofthe non-metallic catalyst material for diamond forms on the surface ofthe respective diamond particles or grains.

The liquid containing the suspended diamond particles or grains isstirred during the drop wise addition. This stirring may be accomplishedby a heater-stirrer and magnetic stirrer, or by an overhead stirrer, orby ultrasonication, or any other suitable method that is ableeffectively to disperse the diamond particles in the liquid.

The diamond powder with precipitated salt may be removed from suspensionand dried at a temperature suitable for removing any residual suspensionmedium or solvents that may be present. The drying temperature maytypically be around 50 to 100° C., or a temperature that does notvolatise the ammonium or halide compound. Alternatively, the diamondwith precipitated salt may be dried under vacuum at a moderatetemperature or room temperature. The diamond with precipitated salt maybe stationary during drying, or may be agitated, tossed or moved in away that increases the efficiency or rate of drying. The diamondparticles and binder material are consolidated to form a green body.

Prior to contact with the binder material, the diamond particles mayhave an average particle size ranging from about 5 nanometres to about50 microns.

The green body, once formed, is placed in a suitable container andintroduced into a high pressure and high temperature press. Pressure andheat are applied in order to sinter the diamond particles together,typically at pressures of around 4 to 7 GPa or more and temperatures ofaround 1000 to 1700° C. or more.

In some embodiments, the grain boundaries of the diamond particles orgrains may contain reduced levels of contaminants that originate fromresidues of the starting salts, thereby enabling strongerdiamond-diamond bonding and improved material properties. In the case ofammonium cations, the lower concentration of contaminants is expectedbecause the ammonium cations will dissociate under sintering conditionsto form hydrogen and nitrogen, which are liberated as gases.

In some embodiments, the sintered PCD may contain an amount of dissolvednitrogen or hydrogen gas. The hydrogen gas liberated during HPHT isexpected to have the beneficial effect of helping to reduce the carbonmonoxide or carbon dioxide intermediate to diamond, thereby enabling theuse of lower pressures and temperatures.

In other embodiments, for example where halides are used, lowerpressures and temperatures may also be used to sinter the PCD. Forexample, 7 GPa or less and 1800° C. or less, as opposed to the moreconventional 8 GPa or more and 2300° C. or more for more conventionalnon-metallic catalyst systems, may be used. Although wishing not to bebound by theory, it is believed that the disruption of the C—O bonds bythe chloride ion reduces the temperature at which the potassiumcarbonate becomes catalytically active.

In some embodiments where, for example, compounds containing an ammoniumcation are used, the anion may be any one or more of the following:carbonates, phosphates, hydroxides, oxides, sulphates, borates,titanates, silicates, halides and the like.

In some embodiments where, for example, compounds containing halideanions are used, the cation may be any one or more of the following:alkali metals, alkali earth metals, and transition metals. Examples ofsuch compounds may include lithium chloride, sodium chloride, potassiumchloride, rubidium chloride, caesium chloride, magnesium chloride,calcium chloride, strontium chloride, barium chloride, yttrium chloride,zirconium chloride, zinc chloride, niobium chloride, all oxidationstates thereof, and mixtures thereof.

In some embodiments, mixtures of ammonium and halide compounds may beused.

The diamond grain sizes in the sintered PCD may range from about 5nanometres to about 50 microns, or from about 20 nanometres to about 20microns, or from about 50 nanometres to about 10 microns. The diamondsize distributions may be monomodal or multimodal.

The non-metallic PCD may be monolithic, or may be attached to a suitablesubstrate, for example a Co-WC substrate. The interface between the PCDand the substrate may be planar or non-planar.

The non-metallic PCD may be leached partly or fully, using anyappropriate leaching process that would be understood by a personskilled in the art.

EXAMPLES

A number of embodiments are described in more detail with reference tothe examples below, which are not intended to be limiting.

Example 1

An approximate eutectic mixture of CaCO₃ and Ca(OH)₂ was mixed withNH₄Cl in the ratio of 0.4 moles CaCO₃ with 0.4 moles Ca(OH)₂ and 0.2moles NH₄Cl. This binder mixture was mixed with diamond in a ratio of4.5 g diamond to 0.5 g binder mixture. This combined mixture was denselypacked into an air tight metal container suitable for HPHT processing.This container was then subjected to HPHT processing to temperaturesabove 1500° C. and pressures above 6.8 GPa and held for times rangingfrom 10 minutes to 60 minutes. It was expected that there would be anintergrown diamond compact after HPHT processing.

Example 2

An equimolar mixture of MgCO₃ and Mg(OH)₂ (in the absence of phasediagrams in the available literature for this system, it was assumedthat an equimolar mixture would be sufficiently close to an eutecticcomposition) was mixed with NH₄Cl in the ratio of 0.4 moles MgCO₃ with0.4 moles Mg(OH)₂ and 0.2 moles NH₄Cl. This binder mixture was mixedwith diamond in a ratio of 4.5 g diamond to 0.5 g binder mixture. Thiscombined mixture was densely packed into an air tight metal containersuitable for HPHT processing. This container was then subjected to HPHTprocessing to temperatures at 1500° C. and pressures above 6.8 GPa andheld for times ranging from 10 minutes to 60 minutes. It was expectedthat there would be an intergrown diamond compact after HPHT processing.

Example 3

An approximate eutectic mixture of CaCO₃ and Ca(OH)₂ was mixed withNH₄Cl in the ratio of 0.4 moles CaCO₃ with 0.4 moles Ca(OH)₂ and 0.2moles NH₄Cl. This binder mixture was mixed with diamond in a ratio of 9g diamond to 1 g binder mixture. This combined mixture was denselypacked into an air tight metal container suitable for HPHT processing.This container was then subjected to HPHT processing to the followingtemperatures: 1600° C., 1800° C., and 2000° C. and a pressure of 8 GPaand held for a time of 10 minutes. It was expected that there would bean intergrown diamond compact after HPHT processing under all of theseconditions.

Example 4

An equimolar mixture of MgCO₃ and NH₄ Oxalate was mixed as a binder withdiamond in a ratio of 4.5 g diamond to 0.5 g binder mixture. Thiscombined mixture was densely packed into an air tight metal containersuitable for

HPHT processing. This container was then subjected to HPHT processing totemperatures above 1500° C. and pressures above 6.8 GPa and held fortimes ranging from 10 minutes to 60 minutes. It was expected that therewould be an intergrown diamond compact after HPHT processing.

Example 5

NH₄ Oxalate was mixed as a binder with diamond in a ratio of 4.5 gdiamond to 0.5 g binder mixture. This combined mixture was denselypacked into an air tight metal container suitable for HPHT processing.This container was then subjected to HPHT processing to temperaturesabove 1500° C. and pressures above 6.8 GPa and held for times rangingfrom 10 minutes to 60 minutes. It was expected that there would be anintergrown diamond compact after HPHT processing.

Example 6

K₂CO₃ and KCl were dried at 50° C. for 24 hours, then were planetaryball milled separately for 45 minutes at 90 rpm, then combined in amolar ratio of 70:30. This mix was combined with diamond powder ofaverage particle size 10 micron in an amount of 5 vol % mix to 95 vol %diamond. Being very hygroscopic, the salt mix was dried between steps aswell as stored when necessary in a vacuum oven. Practical difficultieswith pressure generation were experienced, so that no sintering wasachieved in the experiments. However, it is expected that sintering atgreater than 1000° C. and greater than 7 GPa for more than 5 minuteswill cause sintering, with 1260° C., 7.7 GPa and 1 hour expected toresult in well sintered non-metallic PCD with very good thermalstability and wear behaviour. These temperatures are unusually low forsintering PCD, and this benefit is thought to be due to the presence ofthe chloride ions which may destabilise the carbonate anions andincrease their reactivity as a catalyst material for diamond.

1. A polycrystalline diamond material comprising a mass of diamondparticles or grains exhibiting inter-granular bonding and a bindermaterial comprising a non-metallic catalyst material for diamond, thenon-metallic catalyst material for diamond comprising at least onenitrogen compound derived from an ammonium compound and/or at least onehalide compound.
 2. A polycrystalline diamond material according toclaim 1, wherein the ammonium compound comprises an anion selected fromthe group comprising the carbonates, phosphates, hydroxides, oxides,sulphates, borates, titanates, silicates, halides, and combinationsthereof.
 3. A polycrystalline diamond material according to claim 1,wherein the halide compound comprises a cation selected from the groupcomprising the alkali metals, alkali earth metals, transition metals,ammonium, and combinations thereof.
 4. A polycrystalline diamondmaterial according to claim 3, wherein the non-metallic catalystmaterial for diamond comprises one or more of lithium chloride, sodiumchloride, potassium chloride, rubidium chloride, caesium chloride,magnesium chloride, calcium chloride, strontium chloride, bariumchloride, yttrium chloride, zirconium chloride, zinc chloride, niobiumchloride, oxidation states thereof, and/or mixtures thereof.
 5. Apolycrystalline diamond material according to claim 1, wherein thediamond particles or grains have an average particle or grain size offrom about 5 nanometres to about 50 microns.
 6. A polycrystallinediamond material according to claim 1, wherein the diamond content ofthe polycrystalline diamond material is at least 80 percent and at most98 percent of the volume of the polycrystalline diamond material.
 7. Apolycrystalline diamond material according to claim 1, wherein thepolycrystalline diamond material comprises at most 20 volume percent ofthe non-metallic catalyst material for diamond.
 8. A method for makingpolycrystalline diamond material, the method including providing a massof diamond particles or grains, contacting the diamond particles orgrains with a binder material comprising a non-metallic catalystmaterial for diamond, the non-metallic catalyst material for diamondcomprising at least one ammonium compound and/or at least one halidecompound, consolidating the diamond particles or grains and bindermaterial to form a green body, and subjecting the green body to atemperature and pressure at which diamond is thermodynamically stable,sintering and forming polycrystalline diamond material.
 9. A methodaccording to claim 8, wherein the ammonium compound comprises an anionselected from the group comprising the carbonates, phosphates,hydroxides, oxides, sulphates, borates, titanates, silicates, halides,and combinations thereof.
 10. A method according to claim 8, wherein thehalide compound comprises a cation selected from the group comprisingthe alkali metals, alkali earth metals, transition metals, ammonium, andcombinations thereof.
 11. A method according to claim 10, wherein thenon-metallic catalyst material for diamond comprises any one or more oflithium chloride, sodium chloride, potassium chloride, rubidiumchloride, caesium chloride, magnesium chloride, calcium chloride,strontium chloride, barium chloride, yttrium chloride, zirconiumchloride, zinc chloride, niobium chloride, all oxidation states thereof,and/or mixtures thereof.
 12. A method according to claim 8, wherein themethod includes subjecting the green body in the presence of thenon-metallic catalyst material for diamond to a pressure and temperatureat which diamond is more thermodynamically stable than graphite.
 13. Amethod according to claim 12, wherein the pressure is at least about 4GPa and the temperature is at least about 1000° C.
 14. A methodaccording to claim 12, wherein the pressure is at most about 8 GPa andthe temperature is at most about 2300° C.
 15. A wear element comprisinga polycrystalline diamond material according to claim 1.